\documentclass{standalone}
\usepackage{tikz}
\usepackage{ctex,siunitx}
\setCJKmainfont{Noto Serif CJK SC}
\usepackage{tkz-euclide}
\usepackage{amsmath}
\usepackage{wasysym}
\usepackage{circuitikz}
\usetikzlibrary{patterns, calc}
\usetikzlibrary {decorations.pathmorphing, decorations.pathreplacing, decorations.shapes,}
\ctikzset{bipoles/length=1cm}
\begin{document}
\small
\begin{circuitikz}[>=latex, scale=0.9,european]
  % \useasboundingbox(0.9,0)rectangle(5.1,5);
  \draw(1.5,2.0)--(1.5,1.4)to[pR=$R$,name=hd](1.5,0)[-o]--(1.5,-0.5);
  \draw(1.5,1.4)--(1.5,1.4 -| hd.wiper)--(hd.wiper);
  \draw(1.5,2.0)to[rmeter,name=dlj](-1.5,2.0)to[battery2,name=dc](-1.5,0)[-o]--(-1.5,-0.5);
  \node at(dc)[above left=1mm]{$\mathcal{E}$};
  \node at(dlj.left)[above right]{$-$};
  \node at(dlj.right)[above left]{$+$};
  \node at(dlj.center)[below=5mm]{$G$};
  \node at(dc)[below left=1mm]{$r$};
  \draw[->]([shift=(210:0.3)]dlj.center)--([shift=(30:0.3)]dlj.center);
  \draw[densely dashed](-2.0,0)rectangle(2.5,2.5);
  \draw(-1.5,-0.5)to[bend right](-1.2,-1.0)--(0.3,-2.2)node[midway,sloped,rectangle,fill=red,inner sep=2pt]{\quad\quad\quad};
  \draw(1.5,-0.5)to[bend left](1.2,-1.0)--(-0.3,-2.2)node[midway,sloped,rectangle,fill=black,inner sep=2pt]{\quad\quad\quad};
  \node at (0.45,-1.5)[right=2mm]{黑表笔};
  \node at (-0.45,-1.5)[left=2mm]{红表笔};
\end{circuitikz}
\end{document}